1. Field of the Invention
The present invention relates to a mechanism to dissipate heat from a pluggable optical transceiver, in particular, the invention relates to a structure of a heat sink provided in a cage that receives the pluggable optical transceiver.
2. Related Prior Art
An optical transceiver transmits and receives optical signals through an optical connector engaged therewith by using optically active devices, such as a semiconductor light-emitting device and a semiconductor light-receiving device. An optical transceiver generally has a body that houses a plurality of electronic components, electronic circuits and circuit boards, and also includes an optical receptacle that receives the optical connector. A hot-pluggable optical transceiver is a type of optical transceiver. Such a transceiver is inserted into or extracted from a cage. The cage is arranged on a host board to engage an electrical plug of the transceiver with an optical connector located in the far end of the cage without the need to turn off the power of the host system.
FIG. 6 schematically illustrates one type of the pluggable transceiver called an XFP. FIG. 6 illustrates a state where the XFP transceiver 3 is to be installed within the host board 1. Japanese Patent Application published as JP-2007-156461A discloses an XFP transceiver 3. As illustrated in FIG. 6, the host board 1 includes a bezel 1a and a metal cage 2 that exposes an opening 2a at the front end thereof with respect to the bezel 1a of the host board 1. The XFP transceiver 3 is inserted into or extracted from the opening 2a. The rear end of the transceiver 3 includes an electrical plug 4. The transceiver 3 may electrically communicate with the host board 1 by engaging this plug 4 with an optical connector 5 provided in the far end of the cage 2.
The top of the cage 2 provides a heat sink 6 to dissipate heat from the transceiver 3 set in the cage 2. A clip 7 fastens the heat sink with the cage 2. The contact surfaces of the transceiver 3 and the heat sink 6, such as the roughness of the top surface of the transceiver 3 and that of the bottom surface of the heat sink 6, influence the heat-dissipating efficiency.
Recent transmission speeds in optical communication systems exceed 10 Gbps and sometimes reach 100 Gbps. Such speeds inevitably accompany greater power consumption in electronic and optical devices. An effective heat-dissipating mechanism is always required. To obtain efficient heat conduction between solids, such as the contact surfaces between a housing of the transceiver and a heat sink of the cage, it may be necessary to increase the contact area and to make the contact surfaces as smooth as possible. However, the process to obtain such smooth surfaces is cost-ineffective. Further, outer dimensions of the transceiver, which are primarily defined by acceptable standards, do not permit the contact area to be optionally increased.
Another known method of securing effective thermal contact between metals includes placing a viscous paste or a resin sheet with less hardness between the contact surfaces. Although resin is inherently inferior in thermal conductivity, resin in a form of powder is applicable for merging metals or ceramics with good thermal conductivity by forming the resin in a thin sheet. Such thermo-conducting sheet merges metals or ceramics with good thermal conductivity. Such a thermo-conducting sheet, is applicable as a gap-filler. The thermo-conducting sheet may be placed between contact surfaces of two members rigidly fixed with respect to each other. The thermo-conducting sheet may remove air gaps and equivalently increase the contact area between the members. Accordingly, the thermo-conducting sheet may secure efficient heat transmission between members. However, it is insufficient for effective heat transmission to merely set the thermo-conducting sheet between the members. Additional actions in applying adequate pressure to the members is necessary for effective heat transmission.
In a conventional pluggable optical transceiver, heat-dissipation occurs only by the physical contact between the housing of the transceiver and the heat sink without any thermo-conducting sheet. In other cases where the heat generation in the transceiver is comparably less, the housing of the transceiver itself may perform the heat-dissipating function without coming in contact with the heat sink. However, recent pluggable optical transceivers increasingly generate more heat as the transmission speeds increase and the transmission distance increases. The increases in speed and distance inevitably require heat sinks and an effective heat-dissipating path from the transceiver to the heat sink.
As discussed, the pluggable optical transceiver, as its name indicates, is inserted into or extracted from the cage. Therefore, an arrangement that does not interfere with the insertion or the extraction of the transceiver is necessary for the thermal contact between the housing of the transceiver and the heat sink. When the transceiver is inserted into the cage, the heat sink provided in the cage must be apart from the housing until the transceiver is set in the intended position to secure smooth insertion. Embodiments of the present invention provide such a mechanism between the housing of the transceiver and the heat sink.